i have a couple of questions
1-what is the complete model and serial off of the data plate? I'm assuming it is a Z30/20N RJ (this is the only model i know of that has a rotating jib).
2-when you say articulation jib cylinder are you saying the jib is a rotating jib? or are you talking about the cylinder that raises the jib?
it sounds to me like you are talking about the jib rotator since you mention dowels?
As for working on a rotator motor? I've always sent those out to a hydraulic shop to have them rebuilt/resealed, you'll at least have some sort of workman ship labor and parts warranty if they do it. If you attempt to do it yourself you're on your own.